Glass having dual protective coatings thereon and method for forming such coatings



United States Patent 3,352,707 GLASS HAVlNG DUAL PROTECTIVE COATINGSTHEREON AND METHOD FOR FORMING SUCH COATINGS John Edward Pickard, Selma,Ind., assignor to Ball Brothers Company Incorporated, Muncie, Ind., acorporation of Indiana No Drawing. Filed Jan. 31, 1964, Ser. No. 341,73919 Claims. (Cl. 117-72) ABSTRACT OF THE DISCLOSURE Method for treatingglass by forming two coatings thereon, the first coating being a tinoxide coating produced by exposing heated virgin glass to a heatdecomposable tin compound, and the second coating being a substantiallywater-insoluble polyvinyl alcohol-based coating formed on the tin oxidecoating after annealing, and an article produced by the method.

The present invention relates to a new and improved permanent, lubricouscoating for glass and more particularly relates to an improvedcombination of coatings for glass articles such as glassware, andrelates to a novel rriethod of forming such a combination of coatings ong ass.

Glass articles such as glassware, are handled a great number of timesduring manufacture, inspection, shipping, filling, use, etc. During suchhandling, the ware comes into contact with various mechanical devicessuch as feeders, conveyors, inspection devices and the like and alsocontacts other pieces of ware and surfaces such as boxes, shelves, etc.

This high degree of contact causes damage either by breakage, cracking,scratching or other defacing of the surface thereof. Breakage duringprocessing creates a serious problem in that a processing line may jamwhich requires attention by a person, e.g., to clean the broken warefrom the line. The possibility of interruption of a line due to breakageof ware necessitates a higher degree of supervision than may actually berequired. Breakage during processing is also serious because of thepossibility of slivers or fragments of the shattered glass beingdeposited in adjacent ware which is undesirable in most situations andis completely unacceptable when the ware is to be used for foodpackaging.

Attempts have been made in the past to minimize or eliminate the abovedifficulties by the application of various coatings to glass. While thecoatings proposed, in some cases, have reduced breakage and other damageto some degree, the coatings have created other problems. In some casesit has been difiicult to apply the coating composition to the ware, thecoatings have colored the glass and/ or labels did not tightly adhere tothe coated surfaces. Other coatings did not retain lubricity afterwashing or steam cleaning and thus were unsuccessful. Many coatings werenot acceptable because they had not been approved for use in food. Thus,none of the coatings proposed provided the desired combination ofimproved v properties.

In view of the above and other difliculties and problems with coatingsfor glass heretofore employed, it was completely unexpected andsurprising to discover a new and improved combination of coatings forglass which overcomes many of the problems encountered in the past and,in addition, provides benefits and advantages heretofore unattainable.The coating combination of the present invention provides a permanentlubricous surface on glass which reduces damage during handling to aminimum and which does not lose its lubricity when cleaned with hotwater or steam. Furthermore, the combination provides a surface to whichlabels adhere tightly even after extended periods of storage andhandling. Moreover, the method of coating glass surfaces in accordancewith the invention is simple and convenient and relatively low in cost.Another advantage of the coating combination of the invention is thatthe appearance of the glass is not changed. Moreover, the coatingcompositions employed to form the novel combination of coatings of theinvention are readily formulated and easily applied to glass surfaces.

In accordance with the present invention, glass having a high degree oflubricity and a substantial improvement in strength is formed byapplying a decomposable tin compound to virgin glass which still retainsa portion of its heat of formation and subsequently applying a polyvinyl alcohol-containing mixture thereto and heating the article to anelevated temperature. The glass article so produced has a tin oxidecoating which is believed to be chemically bonded to the virgin surfaceof the glass and an outer coating of a polyvinyl alcohol reactionproduct. Virgin glass or glass in a virgin state is newly-formed glasswhich has not been annealed or had an opportunity to be adverselyaffected by the elements.

The tin compound is applied to the virgin glass while the glass is at atemperature above the decomposition temperature of the tin compound butbelow the solidification temperature of the glass. Advantageously, theglass is between about 900 and 1500 F. and preferably between about 1050and 1300 F. during treatment.

The decomposable tin compound may be either inorganic or organic innature, for example, an inorganic salt such as a tin halide or anorganic tin compound such as an alkyl or aryl tin, an alkyl or aryl tinsalt, etc. Particularly useful are tin compounds such as stannouschloride, stannic chloride, stannous fluoride, diethyl isobutyl tin,dipropyl tin dibromide, etc.

The decomposable tin compound may be dissolved or dispersed in water oran organic solvent prior to application or may be applied as a vapor.Suitable organic solvents for use in forming a coating compositioninclude aromatic solvents, e.g., benzene, xylene, etcx, aliphaticsolvents, e.g., ethyl alcohol, methylethyl ketone, etc.; cycloaliphaticsolvents, e.g., cyclohexane, etc.; and derivatives of such compounds,e.g., nitrobenzene. Advantageously, the composition is an aqueoussolution.

Other materials may be combined with the tin compound provided they donot adversely affect the benefits and advantages of the invention. Forexample, it is advantageous to employ an acid such as hydrochloric acidin an aqueous stannous chloride coating composition. Other materialswhich may be employed include stabilizers, emulsifying or dispersingagents and the like.

The proportion of the tin compound in the coating composition may varyconsiderably depending on the weight of the tin present in the compound.For example, when employing stannous chloride the concentration of thetin salt is advantageously between about 0.5% and 15% by weight of thecomposition. Thus, the proportion of tin in the composition would bebetween about 0.3% and 10%. Similar proportions also are useful withother organic and inorganic tin compounds.

When an aqueous stannous chloride solution is employed, it isadvantageous to incorporate about 0.5% and 6% by weight of hydrochloricacid in the solution.

The tin compound advantageously is sprayed, atomized or vaporized ontothe hot glass surface. Preferably, the

tin compound is applied in a partially enclosed area with an exhaust toremove any undesirable fumes.

The polyvinyl alcohol employed in the second coating composition of theinvention advantageously is a substantially completely hydrolyzedpolymer, that is, a polymer with less than about by weight of residualacetate groups and a saponification number of less than about 40.Preferably, the polyvinyl alcohol has less than about 1% residualacetate groups and a saponification number of less than about 20.

The polyvinyl alcohol is advantageously combined with other materialswhich react with the polyvinyl alcohol to form substantiallywater-insoluble coatings. For example, insolubilizers and plasticizersmay be combined with the polyvinyl alcohol. In addition, various otherpolymers such as polyolefins may be employed with the polyvinyl alcohol.Examples of suitable combinations include mixtures of polyvinyl alcohol,ammonium chloride and a polyhydroxy compound such as glycerin or apolyalkylene glycol; mixtures of polyvinyl alcohol, a polyolefin such aspolyethylene and an organic or inorganic acid or salt, e.g., arelatively strong mineral acid such as phosphoric, hydrochloric, chromicacid, etc.; an aliphatic acid such as carbonic, oxalic, malonic,chloroacetic acid, etc.; ammonium chloride; and the like.

The concentration of the polyvinyl alcohol in the coat ing compositionis advantageously between about 0.001% and 5% by weight of thecomposition and preferably between about 0.05% and 0.2% thereof.Although, com positions containing proportions of polyvinyl alcoholoutside the preferred range produce benefits and advantages of theinvention, the lower concentrations tend to form very thin coatingswhich are less desirable because of the number of coats required, whilehigher concentrations tend to produce compositions of higher viscositywhich make it more diificult to form a smooth, uniform coating.

The proportions of the other components in the composition may varywidely althoughthe polyvinyl alcohol will comprise a substantialproportion of the active ingredients present in the composition. Forexample, the insolubilizer advantageously comprises between about 1 and40% by weight of the polyvinyl alcohol and the plasticizer. betweenabout 3% and 50% of the polyvinyl alcohol. Similarly a polyolefin havinga molecular weight between about 1000 and 3000 advantageously comprisesbetween about 40% and 90% by weight of the polyvinyl alcohol and theacid or salt between about 80% and 300% by weight of the polyvinylalcohol.

In addition to the principal components of the polyvinyl alcohol coatingcomposition as set forth above, other materials :may be included thereinprovide-d they do not deleteriously affect the improved properties andcharacteristics of the coating. For example, a pigment may beincorporated in the coating composition and dispersing above about 160F. Coating of the glass may be con- 1 veniently accomplished as theglass emerges from the cold end of an annealing lehr. However, ifdesired, the composition may be applied to cold glass either before orduring reheating thereof.

The maximum temperature to which the polyvinyl alcohol coating isexposed to complete the required reactions is not critical but islimited only by the temperature which causes the glass to thermo-check,that is, cracking or crazing of the surface. Preferably, the coating isheated to a temperature in the range of about 180 to 500 F.

The invention will be described in detail with reference to thefollowing examples. It is intended that the examples be illustrative ofthe invention and not limiting the invension to the specific proceduresand conditions set forth. In the examples, parts and percentages are byweight.

4 Example I A 5% solution of stannous chloride in water containing about1% hydrochloric acid was sprayed onto a series of 5-ounce baby food jarsas they passed from a forming machine to an innealing lehr. The sprayingwas done at an air pressure of about 40 p.s.i. in an enclosed area witha hood to exhaust any objectionable fumes. The temperature of the jarsduring coating was approximately 1100 F.

After being coated the jars were passed through the annealing lehr andthen coated with a polyvinyl alcohol composition prepared as follows:Eight parts of molten polyethylene having a molecular weight of about2500 were mixed with about 1 part of polyvinyl alcohol containing lessthan about 1% of residual acetate groups and having a saponificationnumber of about 12, 2 parts by weight of polyoxyethylene sorbitanmonostearate and about 20 parts ofboiling water. The mixture wasagitated thoroughly and then added to about 11 parts of the abovepolyvinyl alcohol dissolved in about 200 parts of hot water. Ten partsof the above mixture were then diluted with about 590 parts of water and0.7 part of concentrated phosphoric acid (85% The resulting compositioncontaining about 0.08%

F polyvinyl alcohol, 0.07% polyethylene, and 0.1% phosphoric acid, wassprayed onto a series of S-ounce' glass baby food jars as the jarsemerged from the annealing lehr. The jars were at a temperature of about200 F.

The coated jars were allowed to cool slowly while maintaining atemperature above about F. for about 1 minute.

Samples of the coated jars were selected and control samples were alsoselected from uncoated jars which were made immediately vpreceding andsucceeding the coated jars. The coated jars had a coefficient offriction of about one-fifth that of similar uncoated jars. The jars werealso tested to determine the impact strength and it was found that thecoated jars had an impact strength 10-15% greater than that of theuncoated jars. Labels were applied to samples of the coated jars andfound to adhere tightly even after steam treatment for about 20 minutes.

The jars were used in a processingline. in which each jar was filledwith baby food and processed in a steam cooker at 210 F. forapproximately 10 minutes. The jars moved through the line at a rate ofmore than 500 per minute. No jamming of the processing line occurredwith the coated jars, while approximately one jam per minute due tobreakage or falling down of jars occurred with uncoated jars processedin a similar manner.

The coefiicient of frictionof the coated and uncoated jars afterprocessing was checked again, and it was found that the coated jarsretained the same coefficient of friction as before processing.

Example II The procedure of this example was the same as that of ExampleI, except that a 5% aqueous stannous fluoride solution was employed inplace of the stannous chloride solution. Coated glass jars showedsuperiorities over uncoated jars similar to those exhibited by thecoated jars of Example I.

Example III The procedure of this example was the same as that ofExample I, except that the polyvinyl alcohol coating compositioncontained about 0.1% polyvinyl alcohol having less than about 1% ofresidualacetate groups and a saponification number of about 15, 0.01%ammonium chloride and 0.015% glycerin.

The coated jars were tested according to the procedures of Example I andfound to show the improvements and advantages exhibited by the coatedjars of Example I.

Example IV The procedure of this example was the same as that of ExampleI, except that a 5% solution. of dipropyl tin dibromide in isopropylalcohol was employed in place of the stannous chloride solution. Coatedjars exhibited the superiorities and advantages shown by the coated jarsof Examples I, II, and III.

Example V The procedure of this example was the same as that of ExampleI, except that the polyvinyl alcohol coating composition contained 0.1%chloroacetic acid in place of the phosphoric acid. Coated jars exhibitedimproved lubricity and strength similar to the coated jars of Example I.

The above description and examples show that the present inventionprovides a novel permanent coating for glass which has a high degree oflubricity that withstands treatment with hot water or steam.Furthermore, the strength of the coated glass is substantially greaterthan that of uncoated glass. Another advantage of the coating of theinvention is that the above improvements are achieved withoutsignificantly changing the appearance of the glass and without adverselyaffecting the labeling characteristics of the glass. In addition, themethod of the invention for forming the coatings on glass is simple andconvenient, and relatively low in cost. Further, the coatingcompositions of the invention are easily formulated and can be readilyapplied to glas surfaces.

It will be apparent from the above description that variousmodifications may be made in the compositions and procedures describedwithin the scope of the invention. Therefore, the invention is notintended to be limited to the particular formulations and proceduresdescribed except as many be required by the following claims.

What is claimed is:

1. A coated glass article of improved strength and lubricity having atin oxide coating adhered directly to a surface of said glass articleand a substantially waterinsoluble polyvinyl alcohol coating on said tinoxide coating.

2. A glass article of improved strength and lubricity having a pluralityof coatings, the first of said coatings comprising tin oxide adhereddirectly to the glass article and the second of said coatings comprisinga substantially water-insoluble polyvinyl alcohol reaction productadhered to said tin oxide coating.

3. A glass article as described in claim 2 in which the coating ofsubstantially water-insoluble polyvinyl alcohol reaction productincludes a polyolefin.

4. A glass article as described in claim 3 in which said polyolefin ispolyethylene.

5. A glass article as described in claim 2 in which said polyvinylalcohol reaction product comprises the reaction product of polyvinylalcohol, ammonium chloride and a polyhydroxy compound.

6. A glass article as described in claim 5 wherein said polyhydroxycompound is selected from the group consisting of glycerin andpolyalkylene glycols.

7. A coated glass article comprising a surface of said glass articlehaving thereon a tin oxide coating, and a second water-insoluble coatingon said tin oxide coating, said second coating comprising the reactionproduct of polyvinyl alcohol having not more than 5% residual acetategroups and an insolubilizing agent.

8. An article as described in claim 7 wherein said insolubilizing agentis selected from the group consisting of inorganic and organic acids andsalts.

9. A method of forming a glass article of improved strength andlubricity which comprises forming a tin oxide coating on said glassarticle by applying a heat decomposable tin compound to a virgin glassarticle at a temperature above the decomposition temperature of the tincompound, completing the annealing of the tin oxidecoated article,applying to the tin oxide-coated surface a polyvinyl alcohol-containingmixture comprising polyvinyl alcohol having not more than 5% residualacetate groups and an insolubilizing agent, and heating the polyvinylalcohol coating to an elevated temperature to form a substantiallywater-insoluble polyvinyl alcohol coating.

10. A method as described in claim 9 in which said decomposable tincompound is a tin chloride compound.

11. A method as described in claim 9 wherein said decomposable tincompound is stannic chloride and is applied to said virgin glass articleas a vapor.

12. A method as described in claim 9 wherein said decomposable tincompound is stannous chloride and is applied to the virgin glass articleas an aqueous solution.

13. A method as described in claim 9 wherein said decomposable tincompound is applied to said virgin glass article at a temperature above900 F.

14. A method as described in claim 9 wherein said polyvinylalcohol-containing mixture is applied to said tin oxide coated surfaceat a temperature between about F. and 500 F.

15. A method of forming an improved glas article comprising applying aheat decomposable compound of tin chloride to a virgin glass article ata temperature above about 900 F. to form a tin oxide coating, annealingsaid coated article, applying to said tin oxide coated surface a mixturecontainingbetween about 0.001% and 5% by Weight of polyvinyl alcoholhaving no more than 5% residual acetate groups and an insolubilizingagent, and heating said second coating to a temperature between about160 F. and 500 F.

16. A method as described in claim 15 wherein said insolubilizing agentis selected from the group consisting of inorganic and organic acids andsalts.

17. A method of forming an improved glass article comprising applying avapor of stannic chloride to a virgin glass article at a temperatureabove about 900 F. to form a tin oxide coating, annealing said coatedarticle, applying to said tin oxide coated surface a mixture containingbetween about 0.001% and 5% by Weight of polyvinyl alcohol having nomore than 5% residual acetate group and an insolubilizing agent, andheating said second coating to a temperature between about 160 F. and500 F. to form a substantially waterinsoluble coating.

18. A method as described in claim 17 wherein said insolubilizing agentis selected from the group consisting of inorganic and organic acids andsalts.

19. A method as described in claim 17 wherein said polyvinyl alcoholcontains no more than 1% residual acetate groups.

References Cited UNITED STATES PATENTS Re. 25,767 4/1965 Auffenorde etal. 117-124 X 2,211,323 8/1940 Fordyce 117-161 X 2,577,936 12/1951Waggoner 117-72 2,595,800 5/ 1952 McGraw et al 117-72 X 2,903,377 9/1959Saulnier 117-72 X 3,019,135 1/1962 Orr 117-211 3,033,842 5/ 1962Holtschmidt 117-124 3,085,910 4/1963 Sexsmith 117-72 X 3,141,003 7/1964Neros et a1. 117-124 X 3,199,966 8/1965 OConnell et al. 65-60 X WILLIAMD. MARTIN, Primary Examiner. R- H AC A is a t E am e

1. A COATED GLASS ARTICLE OF IMPROVED STRENGTH AND LUBRICITY HAVING ATIN OXIDE COATING ADHERED DIRECTLY TO A SURFACE OF SAID GLASS ARTICLEAND A SUBSTANTIALLY WATERINSOLUBLE POLYVINYL ALCOHOL COATING ON SAID TINOXIDE COATING.